Download Impact of fertilizers on aquatic ecosystems and protection of water

Aus dem Institut für Pflanzenernährung und Bodenkunde
Ulrich Kremser
Ewald Schnug
Impact of fertilizers on aquatic ecosystems and
protection of water bodies from mineral nutrients
Manuskript, zu finden in www.fal.de
Published in: Landbauforschung Völkenrode 52(2002)2,
pp. 81-90
Braunschweig
Bundesforschungsanstalt für Landwirtschaft (FAL)
2002
U. Kremser and E. Schnug / Landbauforschung Völkenrode 2 (52):81-90
81
Impact of fertilizers on aquatic ecosystems and protection of water bodies from mineral nutrients
Ulrich Kremser1 and Ewald Schnug2
Abstract
Zusammenfassung
Pollution by nutrients from agricultural activities causes many problems in the environment. Fertilization is considered as one of the main sources of pollution of water
bodies caused by agriculture. When high fertilizer rates
are applied which are not in line with the codes of good
agricultural practice, nutrient losses, e.g. by surface runoff, take place which pollute land-based and aquatic
ecosystems.
Fertilizer use, its impact on water bodies and their protection are comprehensively discussed in this contribution. An oversupply with inorganic nitrogen and phosphorus compounds causes an increased nitrification, oxygen
demand, intensification of the primary production of
plankton including „red tides“, excessive growths of
macro-algae and other water plants as well as formation of
the toxic un-ionized ammonia.
The negative impact of nutrient losses from agriculture
on ecosystems in ponds, lakes, rivers as well as to seas and
oceans varies . Oxygen deficiencies in the bottom waters
of shallow areas may result in the production of hydrosulfide which is highly toxic. Low oxygen concentration in
deep water layers where fish spawn may prevent the
development of eggs. Increased density of macro-algae in
shallow waters of seas might affect the composition of
species too.
Defense strategies were developed in order to minimize
the environmental burden caused by agricultural pollution. The so-called end of the pipe solution which means
to clean up the water body after pollution occurred is
rather inefficient in natural waters. A preferable alternative is the reduction or even prevention of pollution, e.g.
by making fertilization more efficient and more environmentally friendly.
Programs for protecting the water bodies against input
of nutrients from agriculture are developed and are being
implemented. Such programs could be supported by concepts like balanced fertilization, ecological agriculture
etc.. The more updated programs are serving a holistic
view and try to combat, minimize or prevent pollution by
nutrients.
Key words: Agriculture, environment pollution, marine
environment protection, nutrients
Einfluss von Pflanzennährstoffen auf aquatische Ökosysteme und Schutz von Gewässern vor Eutrophierung
1 Professional Secretary within the Secretariat of the Helsinki Com-
mission (1996-2001); Federal Environmental Agency, Bismarckplatz
1, 14193 Berlin, Germany, e-mail: [email protected]
2 Institute of Plant Nutrition and Soil Science (FAL), Bundesallee 50,
D-38116 Braunschweig, Germany, e-mail: [email protected]
Die Verschmutzung von Gewässern mit Nährstoffen aus
der Landwirtschaft ist ein schwerwiegendes Problem des
Umweltschutzes. Von besonderer Bedeutung sind hier
Stickstoff und Phosphat, da diese Minimumfaktoren für
das Wachstum von Organismen im Wasser sind. Bekannte Folgen der Belastung von Gewässern mit diesen Nährstoffen sind "rote Fluten", ausuferndes Wachstum von
Riesenalgen und die Freisetzung von Ammoniak. Die
negativen Wirkungen der Eutrophierung sind je nach Art
der betroffenen Gewässer verschieden. Sauerstoffmangel
in den tieferen Schichten flacher Gewässer ist häufig der
Grund für die Produktion toxischen Schwefelwasserstoffs.
Sauerstoffmangel in tiefgründigen Gewässern, die
Fische für die Eiablage bevorzugen, behindert die Entwicklung der Fischbrut. Im Bewusstsein dieser schwerwiegenden Probleme sind eine Reihe von Strategien zur
Vermeidung der Gewässerverschmutzung mit Pflanzennährstoffen entwickelt worden. Darunter ist die blosse
Beseitigung von Umweltschäden die am wenigsten effiziente. Moderne Umweltschutzprogramme zielen auf eine
gesamtheitliche Betrachtung des Problems ab und haben
die Vermeidung des Eintrages von Nährstoffen als Teil der
landwirtschaftlichen Produktionstechnik zum Ziel.
Schlüsselworte: Landwirtschaft, Meeresumweltschutz,
Nährstoffe, Umweltverschmutzung
82
1 Introduction
Pollution by nutrients from agriculture causes many
problems in the environment. One of the main sources of
these problems are fertilizers. Industrial production and
the usage of fertilizers have led to a sharp increase in food
production that has been accompanied by the population
growth in almost all countries around the world. While
fertilizers restored into soil have had the requested affect,
considerable amounts of fertilizers are carried to landbased and aquatic ecosystems by leaching, surface run-off
and other processes. These ecosystems have been adversely affected by nutrients.
Assumption that a stabile food supply in the future is
essential, means that nutrients have to be added to agroecosystems and fertilization has to be continued. Nevertheless, one should try to minimize the adverse impact of fertilization to the environment.
The topic of this paper is the impact of fertilizers on different aquatic ecosystems as well as how to protect water
bodies. A brief historical review shows that there is a
strong correlation between soil fertility, industrial production of mineral fertilizer, food production and population
growth. This contribution will also prove the rising awareness on environmental issues worldwide in the second half
of the century. Aquatic ecosystems are described with
respect to nutrients and trace element contents under so
called natural conditions. Comparison with the actual
nutrient and trace elements conditions should take place
and the adverse impact of fertilizers on the ecosystem
should be explained. A clear distinction between direct and
indirect effect seems to be helpful. The focus here are
marine ecosystems, and in particular those of coastal
zones and regional seas. Finally, concepts and programs
on how to protect water bodies from nutrient discharges
from agriculture are presented.
2 Brief historical review
2.1 Soil fertility and population growth
For millions of years people have made their living by
hunting, fishing and picking. With transition in the relationship between man and his means of sustenance from
nomadic to permanent settlement, from the existence
mainly based on hunting and picking to one mainly based
on agriculture and animal breeding, an important change
took place. This process became prerequisite for the division of labor, development in trade and science, urban
settlements and higher organizational and administrative
structures within tribes. The emergency of agriculture was
a lengthy process which started in the Neolithicum in the
Near East and spread to other regions.
A relatively high and stabile food production from agriculture accelerated population growth, which conversely
increased food demand. Some regions benefited from natural fertilization like Egypt where the floods of the river
Nil renewed the fertility of the soil almost each year. Climatic variations, i.e. unfavorable weather conditions led to
famines, and together with wars reduced the population
number. Since fertility was low in large areas of the earth
and people at that time did not know how to improve that,
agricultural fields had to be extended mainly by deforesting. In safeguarding food supply agricultural measures
strongly affected the nature. In parallel, remaining forests
were used for agriculture and animal breeding, but at the
same time forests were partly damaged in Europe in the
Middle Ages because of lack of maintenance.
Maintaining or improving the fertility became more
important along with further population growth. Discovery in 1847 by the German agricultural chemist Justus von
Liebig, that all the nutrients plants removed from the soil
could be restored in mineral form, was the basis for farreaching changes. It took some hundred years more until a
comprehensive usage of fertilizers took place. Already in
the second half of the 19th century population growth in
cities around the Baltic Sea took place with a sharp and
strong increase after 1880 (Oden, 1980).
The global use of fertilizers increased from 14 mill.
tons/y to 146 mill. tons/y between 1950 and 1989, and
during the same period of time the grain production nearly tripled (Brown, 1997). World population grew from 2.5
billion in 1950 to about 5.5 billion in about 45 years
(Flavin, 1997). In the mean for the whole world, and in
most regions of the world the increase of food production
overcame the population growth during the last half century. Only in the Sub-Saharan Region the basic argument
by Thomas Malthus (1766 - 1834) that natural resources
could not assure such an expansion in food supply that
would match the population growth was proven correct.
Despite this optimistic view concerning the security of
the global food supply there are also other views and
developments which might slow down the optimism for
the future (Pinstrup-Anderson et.al., 1997). These are
among others:
•
•
•
•
ongoing population grow
growing water scarcity
possible climatic changes
declining soil fertility
2.2 Rising awareness regarding agricultural impact to
nature and ecosystems
The impact of agriculture to nature did not happen over
night. Over the centuries agricultural activities have been
considered as cultivating and civilizing measures only.
U. Kremser and E. Schnug / Landbauforschung Völkenrode 2 (52):81-90
It is perhaps surprising that the relation between agriculture and environment has not been very widely taken
into account since a huge fraction of arable land has been
used for planting and animal husbandry. Deforesting has
led, at least under humid climate conditions to changes,
e.g. land to be used for agriculture, and reduction in biodiversity are considered positive or neutral (Kevles, 1997).
Some adverse impact to the water bodies was recognized
in the early stage. Trivial changes were first defined to the
immediate vicinity of urban areas. In the Baltic region,
industrialization and especially that one based on forestry,
like pulp and paper mills, but also the increasing use of
Table 1
Regional Seas Conventions
Adopted
Convention
1972
Convention for the Prevention of Marine
Pollution by Dumping from Ships and Air
craft (Oslo Convention; North Sea and N-E
Atlantic)
1972
Convention for the Prevention of Marine
Pollution by Land-based Sources (Paris
Convention; N-E Atlantic)
1992
Convention for the Protection of the Marine
Environment of the North-East Atlantic
1974 and 1992
Convention on the Protection of the Marine
Environment of the Baltic Sea Area
(Helsinki Convention; Baltic Sea)
1976
Convention for the Protection of the
Mediterranean Sea against Pollution
(Barcelona Convention)
1978
Kuwait Regional Convention for Coopera
tion on the Protection of the Marine Environment from Pollution
1981
Convention for Cooperation in the Protection and Development of the Marine and
Coastal Environment of the West and
Central African Region
1981
Convention for the Protection of the Marine
Environment and Coastal Area of the
South-East Pacific
1982
Regional Convention for the Conservation
of the Red Sea and Gulf of Aden Environment
1985
Convention for the Protection, Management
and Development of the Marine and Coastal
Environment of the Eastern African Region
1986
Convention for the Protection of the
Natural Resources and Environment of the
South Pacific Region
1992
Convention on the Protection of the Black
Sea against Pollution
83
fertilizers were the main reasons for a strong increase of
nutrient input since the turn of this century (Dybern et al.,
1981). For centuries the way of re-circulating organic substances within agriculture in China and may be other
Asian countries too, has been used as good example. By
different reasons these way of thinking seems to go to be
forgotten now, in the 21st century.
General doubts about the validity of the one-sided
assessment of the role of agriculture in preserving environmentally sustainable development arose rather late in
Europe in the second half of the 20th century. Strong
increase in the food production and population growth in
conjunction with the increasing fertilizers and pesticides
use strengthened the impact to the environment, in particular to water bodies. Industrial pollution, culminating in
catastrophes like Minamata illness in Japan, 1956, and the
impact of pesticides to birds (reflected e.g. in „Silent
spring“ by Rachel Carson, 1962) led to a rising awareness
and paved the way for investigations in different seas and
regions with an aim to clarify the actual state of pollution.
Working group under ICES (International Council for the
Exploration of the Sea) to investigate the state of pollution
in the Baltic Sea was established in 1968, and the working
group found the Baltic Sea heavily polluted (ICES, 1970).
Similar conclusions were drawn concerning other sea
areas, too. These results have been discussed at different
national and international meetings, and measures which
should include curative and preventive means to fight pollution were demanded. Under the pressure of the public
awareness international agreements and conventions were
concluded few years later (Table 1), beginning in Europe
and shifting to other areas. This development culminated
in 1992 when the Rio-Conference took place.
3 Soil fertility and natural composition of nutrients in
soil and water
3.1 Natural concentrations of nutrients in soil and water
Plantuire, among others, macro and micro nutrients for
growth. If a plant is harvested and picked up from the
ground the soil becomes impoverished in substances. To
keep the soil fertile, nutrients have to be restored to soils
by fertilization.
Concentrations of nutrients in the soil and water vary
significantly pending on the basic material (rocks and
weather beaten rocks) modified during millions of years
by climatic and other conditions. River waters are naturally rich in those elements and substances available and soluble in the hydrological basin and, to a certain extent, in
the atmosphere. So, we can not speak about nutrients’ concentration in a „mean soil“ or a „mean river“ but to define
the concentration of nutrients in the soil and water optimal
for the agricultural purposes or the sustainability of
ecosystems.
84
Table 2
Concentrations of major constituents (eleven) and of some trace elements in the ocean with 35 ‰ salinity (after Nehring, 1969 and
Grasshoff et. al., 1981)
Major
constituents
g/kg
Trace
elements
mg/l
Chloride (Cl)
Sodium (Na)
Sulphate (SO4)
Magnesium (Mg)
Calcium (Ca)
Potassium (K)
Hydrogen carbonate
Bromide (Br)
Boron (H3BO3)
Strontium (Sr)
Fluoride (F)
19.345
10.752
2.701
1.295
0.416
0.39
0.145
0.066
0.027
0.013
0.0013
Iron
Zinc
Molybdenum
Manganese
Copper
Arsenic
Cadmium
Nickel
Chromium
0.01
0.01
0.01
0.002
0.003
0.003
0.0001
0.0005
0.00005
Elements to be found in fertilizers are in bold
The annual run-off from land to ocean is about 50 000
km3. Depending on the special conditions in the hydrological basin rivers carry substance, including nutrients, into
oceans. Due to big water amount in the oceans the contribution by rivers (and other sources at the ocean floor) is in
the magnitude of 10-5 per year only and the composition of
sea water remains very stabile over long periods. All
known chemical elements are solved in the ocean, but in
different concentrations. Only eleven of them, Na, K, Mg,
Ca, Sr, Cl, S, inorganic C, Br, B and F (major constituents)
round up to about 99 % of the whole salinity. This group
includes the main fertilizer components except nitrogen
and phosphorus and boron, a trace element. There is a stabile relation between chlorine content and salinity in sea
water, which makes it possible to indicate the amounts of
the other major constituents after measuring the chlorine
content.
Nitrogen and phosphorus are not defined as major constituents of sea water and their relation to chlorine is not
fixed. Their concentration and distribution differ in the
Indic, Pacific and Atlantic Oceans. In the surface layer of
the oceans the nitrate concentration is about 1-2 mikrogrammatom/l and increases to 20-40 with depth. When
such nutrient rich water reaches the surface (up-welling),
high biological productivity can be observed.
4 Impact of fertilizers on aquatic ecosystems
4.1 General remarks
Large amounts of nitrogen and phosphorus are carried
via rivers into the seas and oceans. Atmospheric transport
of phosphorus is almost negligible. The percentage of airborne nitrogen depends on many factors like industrialization, traffic, climatic conditions etc. About one third of all
nitrogen input into the Baltic Sea is estimated to be airborne and the percentage is similar for the North Sea and
the Mediterranean. Nitrogen deposition in Europe roughly
originates both from nitrogen oxides and ammonia. While
nitrogen oxides mainly originates from power plants and
traffic, it has been estimated that the agricultural sector is
responsible for more than 90 % of ammonia emissions
(HELCOM, 1997b; Swedish Board of Agriculture, 1995).
Animal husbandry in conjunction with the production and
usage of manure contributes between 80 and 90 % to these
emissions but, commercial fertilizers are estimated to be
responsible for about 10-15 %.
The input of nitrogen means permanent and additional
fertilization, which might not be harmful as long as this
does not exceed the critical load. The critical load for
eutrophication nitrogen is defined as „a quantitative estimate of an exposure to deposition of nitrogen as ammonia
and/or nitrate below which harmful effects in ecosystem
structure and function do not occur according to present
knowledge“ (EMEP, 1997) and, has to be seen in line with
sulfur and nitrogen deposition of acidifying compounds.
4.2 Aquatic ecosystems
Rivers:
Rivers collect water from the hydrological basin and, on
its way trough soil, rocks etc. resolve substances containing nutrients and trace elements. Water is used for human
activity and the input of untreated and treated waste water
from municipalities and industries as well as from agricultural activities has made rivers strongly polluted. The
increase in nutrient input from agriculture into rivers has
become often three-fold or more over the last three or four
decades and is well recognized in many countries (Loigu,
1989, Enell et.al, 1989). Rivers are not fertilized but there
is a strong indirect impact of fertilization to the ecosystem,
i.e. not the fertilizer itself but the effects caused by it are
the reason for the impairment. For inorganic nitrogen and
phosphorus compounds the indirect impacts are:
- nitrification oxygen demand because of the microbial
oxidation of ammonia
- intensification of the primary production of plankton,
macrophyta and other water plants by increased availability and use of nutrients
and finally
- formation of the toxic ammonia (NH3),
which is indirectly supported by fertilization assuming
that the above mentioned intensification of primary production produces big amounts of organic material containing nitrogen which is mineralized to the ammonium
ion. The percentage of not ionized ammonia in the total
ammonia (NH4 + NH3) essentially depends on the pHvalue and the temperature of the water (Hamm,1991). In
eutrophic waters daily variations often raised with the pHvalue to more than 9 which shifts the balance of the total
ammonia towards unionized ammonia. Unionized ammo-
U. Kremser and E. Schnug / Landbauforschung Völkenrode 2 (52):81-90
nia is toxic to fish, vertebrates and plants. Another effect
of the eutrophication is, among others, a possible rise in
water level by an excessive growth of macrophyta in conjunction with increasing friction. The ecosystems in the
water course as well as at the banks will be affected, too.
Lakes:
Lakes have their own hydrological basin or, they are in
the course of a river, i.e. they are similar to rivers as far as
the fertilizer impact is concerned. Again, as there is no
direct impacts and the indirect ones are those valid in
rivers as well (e.g. the indirect effects by ammonia in conjunction with high pH-value and temperature). The important difference is, of course, that the residence time indicating the mean period a water molecule and other substances remain in the water body. Therefore, rivers damaged by the pollution can be cured much faster than lakes
which keep the substance longer. In the most unfavorable
case, i.e. if a lake (or pond) has no outflow then the substances in the water are trapped and even small amounts
given constantly over long periods will lead to high concentrations if there are no or only small sinks for that substance. The result is that lakes become vulnerable to nutrients and the effect of the eutrophication is observed as
green belts in the shallow waters by reed and macrophyta.
Additionally, phytoplankton covers the lakes’ surface. A
high primary production generated by the availability of
nutrients causes high oxygen demand in the course of mineralization of the organic material. Anoxic conditions
make life impossible both for the animals and plants, i.e.
the ecosystem be will destroyed.
Seas and oceans:
Oceans receive lots of substances via rivers resolved in
the water or transported as unsolved material by friction.
Additionally, different substances are deposited from the
atmosphere. Due to the relatively small annual amount by
rivers and by the atmosphere in comparison to the amount
already resolved in the oceans , the concentration of chemical elements in the oceanic waters is rather stabile over
long periods. That does not apply to the coastal areas
which are influenced by river waters and, in particular by
nutrients. Coastal areas often are affected by eutrophication. There is also concern about the increasing input of
nitrogen into the oceans in particular into parts where
nitrogen is the limiting factor of biological growth (for
example the Antarctic waters). Eutrophication can also
cause explosive blooming of algae - „red tides“ - which
cover the surface of the sea and are responsible for huge
losses in commercial fisheries. There are indications that
the blooms, toxic or otherwise, are increasing (GESAMP,
2001a). On the other hand there are proposals even to fertilize sea in order to activate the growth of phytoplankton
85
and to increase fish catches (see under 4.4 : Baltic Sea in
conjunction with the effects of eutrophication on fishery).
4.3 The example of the Baltic Sea
The Baltic Sea receives annually about 480 km3 fresh
water via rivers and about 260 km3 by the precipitation
(Fennel, 1996). Rivers contain chemicals and other material from the hydrological basin of the Baltic Sea which is
about 1.72 Mill. km2 and populated by more than 80 million people with strong agricultural and industrial activities.
The annual total nitrogen (N) input into the Baltic Sea is
estimated to be around one million tons and phosphorus
(P) input around 50 000 tonnes. The main sources of N
within the Baltic Sea catchment are agriculture, municipalities, industry, power plants and traffic and, of P agriculture, municipalities and industry (HELCOM, 1995;
Kremser, 1997). The importance of these sources varies
from one country to another according to the economic
structure and standards.
Nutrients are mainly carried into the Baltic Sea via
rivers, about one third the N load is estimated to be airborne. Also, the contribution via groundwater and direct
discharges cannot be neglected. The atmospheric load of P
to the Baltic Sea is almost negligible. To balance the nutrients load in the Baltic Sea is more complicated, e.g.
immobilization, remobilisation and other interaction as
well as the water exchange between the Baltic Sea and the
North Sea have to be taken into account. Other sources
and sinks estimated by Nehring et al. (1996) and, mainly
based on investigations under HELCOM indicate that
ships and fisheries as nutrient sources for such a balance
are negligible. Denitrification counts for losses of about
470 000 tons and the profit by N2 -fixation is estimated to
be 130 000 tons per year. The net balance for N by the
water exchange with the North Sea is 150 000 tons leaving the Baltic Sea annually, and, for P zero.
These estimations are based on measurements, calculations and extrapolations using plausible assumptions. As
the natural processes show strong variations in time and
space the figures have to be interpreted on the basis of the
statistics. For instance, the nitrogen input into the Baltic
Sea via rivers correlates strongly with the river discharges
and, a single value or a mean considered over a year only
might be misleading. This suggests that the nitrogen losses from arable land are partly generated by surface run-off
in conjunction with a heavy rain or melting waters
(Nehring et al., 1996).
Among all nutrient sources agricultural activities are
very important. The drastic increase in the fertilizer use
since the 50’s in the Baltic Sea Catchment area correlates
highly with the mean phosphate and nitrate concentration
during winter in the Bornholm Basin and, certainly in
other basins as well.
86
As mentioned earlier the particular conditions of the
Baltic Sea including the fresh water discharge by rivers
result in somewhat different concentrations of trace metals
in the Baltic Sea in comparison with the oceans. Additionally, there is an anthropogenic input by municipal and
industrial waste water, by atmosphere as well as by agricultural activities. In most cases the concentrations of
trace metals in the Baltic Sea are smaller than in the North
Sea and in all cases much smaller than required by the
drinking water standards. Consequently, there are no toxic
affects to the animals and plants (Kremling, 1996).
An excess of nutrients mainly causes eutrophication,
increased plankton biomass and oxygen deficiencies in the
bottom water of shallow areas and of basins. In the Baltic
Sea about 30 phytoplankton species have been proved to
be harmful, e.g. cyanobacteria which can affect fish and
birds. Even cattle and dogs have died after being intoxicated. In 1988 the bloom of Chrysochromulina polylepis
caused trouble to fish farms and, killed marine organisms
(HELCOM, 1997a; Lenz, 1996). It can be argued that the
increasing frequency of harmful blooms in the Baltic Sea
generated by the nitrogen input from agricultural activities
might correlate with the changes in the Redfield N:P ratio.
Such events as, for instance, toxic algal blooms are normally very well reported in the media and they also disturb
tourism.
Another field affected by the eutrophication is fishery.
Heavy algae blooms and mass development of plants and
marine organisms can affect fishing process even mechanically. At the beginning of the century the annual fish
catches were about 100 000 tons. Up to the World War II
the amount rose slightly and has increased steeply since
the 50’s. A maximum yield was reached in 1984 amounting roughly to one million tons. This development certainly took place parallel to the eutrophication due to the nutrient input to the Baltic Sea and the rise in primary production (Thiel el al., 1996). Later on the catches decreased to
some 600 000 tonnes (Thurow, 1980; Rechlin, 1996)
caused by over-fishing of cod and economic/commercial
reasons.
This development is mostly considered to be positive by
the fishery sector itself. However, there has been observations on changes in the structure and composition of fish
stocks, which relates to the eutrophication. One example is
the opposite development of pike and pike-perch stocks,
e.g. the population of pike is dropping while that of pikeperch’s is increasing because of the improvement in the
conditions for pike-perch that prefers muddy coastal
waters when pike does not. Drastic drop in the catches and
even disappearance altogether have happened with some
other fish in the Baltic Sea as well.
The decrease of macrophyte in coastal areas has reduced
the reproduction of fish that needs these plants for the eggs
to grow up. Moving to other areas - often to more shallow
ones with acceptable plants - can lead to high density of
eggs and the reproduction can be threaten by oxygen deficiency. The probability for the oxygen deficiency in shallow and deep waters of the Baltic Sea is increased by the
eutrophication. A high primary production produces big
amounts of dead organic material which sinks down to be
mineralized in the bottom. The mineralization needs oxygen from the water, e.g. the oxygen content in the water is
diminishing if there is no other source to compensate the
loss. The vertical transport of oxygen in the Baltic Sea is
impeded due to the increased water density with depth.
Therefore, the only source to bring fresh salinity and oxygen to the deep waters in the Baltic Sea basins is major
inflows of saline water, which occurs at irregular intervals
(HELCOM, 1997a).
Certain fishes, like cod have the reproduction area in
the deep basins and, they are adjusted to certain salinity,
water temperature and oxygen content. Reproduction gets
complicated if the oxygen content is less than 2 mg per
liter (Schnack, 1996). Needless to say that all life except
bacteria will be destroyed if the conditions become anoxic.
Due to the increased fish catches in conjunction with the
eutrophication it has been proposed to promote the primary production by fertilization in seas and parts of the
oceans (Hoell, 1996). The state owned Norsk Hydro has
launched a five year research program called Maricult,
designed to consider the cultivation of marine ecosystems
for a more comprehensive use of the oceans and the sustainable harvest of marine resources in the future. This
includes the addition of nutrients. As learnt from the
example of the Baltic Sea an addition of nutrients means
an increase in the primary production. But that would be
only one side of the coin the other one being, inter alia, an
unpredictable change of marine flora and fauna. Additionally, it is in contradiction to the letter and spirit of international agreements to tackle nutrient inputs to the marine
environment (Lutter, 1996).
4.4 Other regional seas
From the example of the Baltic Sea the following can be
generalized: Nutrient load into waters may lead to:
- intensification of primary production
- intensified oxygen demand
- deterioration of the ecosystem.
Despite the basic processes in different waters are the
same the results vary because of differences in e.g.
- basic characteristics of the sea, in particular related to
exchange conditions with the open sea and interaction
with the sediment (immobilization, remobilization)
- climatic conditions
- human activities (e.g. fishery and other sinks regarding
the nutrient balance).
Therefore the “visible” impact of nutrient load to
regional seas varies and this fact also affects the ranking of
U. Kremser and E. Schnug / Landbauforschung Völkenrode 2 (52):81-90
pollution from agricultural sources in the regional seas
programs. In these programs nutrients are regarded as priority issue only for the Black Sea (and the Baltic Sea)
whereas other regional seas programs classify nutrients as
less important.
87
Helsinki Commission, HELCOM). It was an encouraging
step forward in times the cold war divided the Baltic Sea
and most countries located around the Sea into NATO- and
Warsaw-Treaty members.
5.2.1 The Helsinki Convention
5 The protection of water bodies
Despite agricultural activities always have been a burden to nature it took centuries to acknowledge this truth.
Agriculture and fertilization became a problem in the second half of the 20th Century at least in Europe and certainly in America too in line with strong increase of food
production, fertilization and population growth. Now it
has been officially recognized as a problem in Europe and
world wide and it can be considered as first step for dealing with the problem properly.
5.1 Mineral fertilization and protection of water bodies
Since stabile food supply in future is essential, mineral
fertilization has to be continued. But one should try to
minimize the adverse impact to the environment - otherwise the basis of our life will be destroyed. With other
words:
There is no alternative to fertilization and no alternative
to protecting the environment and the water bodies.
The impact of fertilization to water bodies could start
from
• improving the efficiency of fertilization and
• taking measures for protecting the water bodies.
Improving the efficiency could be achieved by coating,
granulation of the fertilizers, precision agriculture, tailor
made compositions of the fertilizers etc., which should not
be discussed further here. Measures for protecting the
water bodies are dealt with in the following chapter.
5.2 The protection of the marine environment of the Baltic
Sea (as an Example)
Measures for protecting the water bodies as such means
to decrease the nutrients run-off into the water bodies by
other means, what should be described at the example of
the Baltic Sea.
The Baltic Sea has a long history in dealing with pollution problems which started in 1968 (see chapter 2.2). The
outcome of the first pollution checking of the Baltic
waters were considered on national and international level
and lead in the consequence to the UN Conference on the
Human Environment held in 1972 in Stockholm, Sweden.
First time in history environmental protection has been
considered a problem of global dimension.
This development resulted in signing regional seas conventions, among them the Convention on the protection of
the marine environment of the Baltic Sea ( 1974 and 1992,
The Baltic Marine Environment Protection Commission
(see homepage of HELCOM: www.helcom.fi) works
through the Commission, the Secretariat, Working Groups
and projects. In 1992 the Program Implementation Task
Force (PITF) for coordinating the implementation of the
Baltic Sea Joint Comprehensive Environmental Action
Program (JCP) which is working within the framework of
the HELCOM has been established.
One of the strongest tools of HELCOM is to elaborate
and adopt Recommendations.
There are different means by the Helsinki Commission
for reducing the nutrient load into the Baltic Sea. It is done
mainly by
• Recommendations related to agriculture, marine and
land-based transport and industry as well as by
• implementing the JCP.
The Recommendations become legally binding after
having transferred into national law for implementation in
the countries. Monitoring and assessment of the load
(sources and paths), concentrations in water bodies etc. are
organized under HELCOM working groups. The implementation of the JCP is done by the countries with support
by the International Financial Institutions and other governmental and non-governmental organizations and institutions.
During the first years of existence HELCOM focused on
issues like
• safety on sea
• prevention and combating of oil pollution
• reduction of pollution by harmful substances.
It took until 1986 until the first Recommendation (7/2)
on agriculture was adopted, titled „Measures aimed at the
reduction of discharges from agriculture“ (Full text of
Recommendations: See home page of HELCOM).
In this Recommendation is taken note of the fact that
increasing concentrations of nutrients in the marine environment cause negative effects on ecosystems including
eutrophication and oxygen depletion. Furthermore, the
importance of discharges from agriculture as source of
pollution of the marine environment by nutrients is recognized. Fertilization plans and water protecting zones are
demanded.
Regarding reduction of nutrient input into the Baltic
Sea a mile stone was set in 1988 by the Ministerial Declaration which demanded a reduction of loads of harmful
substances nutrients by about 50 % until 1995 based on
the 1988 figures.
88
Inspired by that Declaration new agricultural Recommendations recognized diffuse sources as substantially
contributing to the eutrophication problem. Artificial fertilizers should be applied according to crop need promoted by economic incentives. Fertilizer and crop-rotation
planning and prognosis tools for nitrogen and phosphorus
application should be taken into account (HELCOM Recommendations 13/9 and 13/10). Sufficiently broad vegetation zones (filter strips) along water courses should be
considered as an additional measure.
The Contracting Parties are obliged to report on the
implementation to the Commission.
In 1996 the Baltic Sea Summit addressed, inter alia, the
pollution from agricultural sources and called for urgent
elaboration of an annex on agriculture to the Helsinki
Convention. This work was done by a HELCOM Project
on Agriculture and adopted as HELCOM Recommendation 19/6.
The annex stated that agricultural activities within the
catchment area of the Baltic Sea are responsible, inter alia,
for pollution of water and air by nitrogen, phosphorus and
plant protection products, causing negative effects on the
Baltic Sea ecosystem including eutrophication, oxygen
depletion and reduced biological diversity. The Recommendation lists up different requirements, e.g. on application rates for nutrients and refers to water protection
measures and nutrient reduction areas.
The situation regarding pollution from agricultural
sources could not be solved immediately and it was stated
that this problems needs permanent attention.
5.2.2 Recent and at present activities of HELCOM related to agriculture
In 1999 HELCOM reacted on the need to focus on
reduction of nutrient input to the Baltic Sea and established a Working Group on Agriculture. The main issues
of the Working Group are aimed at combating eutrophication of the waters by implementing the Annex III to the
Convention and by elaborating and implementing national
Codes on Good Agricultural Practice in the countries concerned. The working program includes also issues like balanced fertilization and ecological farming.
Following the agreements by the Rio-Conference and
based on the knowledge that environmental and social
problems are connected, the overall development is now
aimed at sustainable development. In the Baltic Sea
Region additional activities are taken towards sustainability by the Baltic Agenda 21 which comprises eight sectors
among them agriculture. A huge GEF Baltic Sea Regional
Project also contains a strong agricultural component and
is linked to HELCOM and to Baltic 21. The HELCOM
Working Group on Agriculture has the coordinating function regarding agriculture in the Baltic Sea Region.
5.2.3 Results of HELCOM activities towards reduction of
nutrient loads into the Baltic Sea
The Ministerial Declaration 1988 demanded, inter alia,
the reduction of input of nutrients into the Baltic Sea by
about 50 % until 1995. The target was not achieved as a
statistical mean taken over the entire catchment area of the
Baltic Sea. However, several countries reached the goal,
supported by adverse economic conditions (which made
the use of fertilizer to expensive for the farmers). Due to
additional measures implemented, the target of 50 %
reduction is planned to be achieved in 2005.
The implementation of the JCP contributes to the overall goal of reducing the nutrient load to the sea. When
launching the program, areas and sites of high emission or
discharges from one or more point- and/or diffuse sources
were classified as Hot Spots (Kremser, 2001). Originally
132 Hot Spots located in the catchment area of the Baltic
Sea were listed, among them 17 agricultural ones.
Between 1991 and 1998 the emissions and discharges
from Hot Spots have been reduced by 39 % (Phosphorus)
and by 28 % (Nitrogen). One agricultural Hot Spot was
deleted from the list in the year 2001 and others are
expected to be deleted soon.
The reductions as indicated above are also reflected in
the improvement of the water quality in the coastal waters
(HELCOM, 2001, Fourth Periodic Assessment). The interpretation mainly points to achievements in the wastewater
sector in connection to municipalities and industry and
less to agricultural activities including fertilization.
Despite the dramatic decrease of use of mineral fertilizers
over several years in some countries in the hydrological
basin of the Baltic Sea (countries in economic transition),
the nutrient runoff remained almost the same.
5.3 The protection of the marine environment of other
lakes and seas
There is the question what message could be taken from
the experience of the Baltic Sea region and transferred to
other regional seas in order to be used there. The answer
seems to be easy:
There is the need to have programs based on international agreement and – if possible – to make it legally
binding (like a Convention). Implementing the program
needs international cooperation and a solid financial basis.
The latter one is not always the case as reflected in the rating of financial status of regional sea and action plans by
UNEP (Table XX: Third global meeting of regional seas
and action plans, Monaco, 2000).
The example of the Baltic Sea, i.e. the implementation of
both the Helsinki Convention and the JCP, has been very
successful. That is why the programs are
• targeted to a convincing goal: The protection of the Baltic Sea and the restoration of the ecosystem,
U. Kremser and E. Schnug / Landbauforschung Völkenrode 2 (52):81-90
• adjusted to the specific environmental problems, struc-
tured in order to safeguard a long-lasting progress,
• have been up-dated from time to time in order to adjust
to the changed political, social, economic, environmental, etc. conditions,
• the partnership does include the governments, national
authorities on local, regional and national level, the
International Financial Institutions (IFI´s), donors, private sector and NGO´s and
• the implementation of the programs is directly related to
a sustained political commitment and broad-based
public support in the region.
6 Conclusions
The purpose of agriculture is to guarantee a secure food
supply and this requires fertilization. Preserving the environment including marine ecosystems is of the same priority as agriculture.
Fertilization causes few direct but many indirect effects
which impair ecosystems. The eutrophication of rivers,
lakes and seas is considered as one of the important environmental problems, generating or/and supporting oxygen deficiency, production of toxic NH3, algal blooms,
change in spatial distribution of marine organisms,
increase and depletion of fish stocks, change in reproduction conditions for fish and marine fauna etc.
Fertilization is one factor among the agricultural activities being responsible for the decisive percentage of the
whole nutrient input to the marine ecosystems via atmosphere, rivers etc. The example of the Baltic Sea shows that
adopting and implementing tailored programs for reducing the nutrient input is eventually a successful way.
Many other Regional Seas have much better mixing
conditions as the Baltic Sea and the exchange with the
open waters gives the impression that the nutrient input is
not really a threat to the ecosystems. This impression,
however, is illusive! Human beings think linear but the
nature interacts non-linear, i.e. we even do not know
where we are at the moment with respect to the change of
mode.
Consequently there is the demand to preserve the marine
ecosystems. It needs action now which is supported, inter
alia, by the IMO/FAO/UNESCO-IOC/WMO/WHO/
IAEA/UN/UNEP Joint Group of Experts on the Scientific
Aspects of Marine Environmental Protection (GESAMP).
This working group concluded that land-based activities
are the major sources of problems and threats facing the
oceans, especially coastal areas, except for the effect of
fishing and the threats posed by global climate change
(GESAMP Reports and Studies No 71, 2001):
„In the past decade, there have been some notable successes in curbing the negative impacts on land-based
activities on the marine and coastal environment. Unfortunately, from a global perspective, the degradations of the
89
oceans and coastal areas has continued, and in many
places even intensified. Degradation is much more severe
in the coastal areas than in the open ocean.
The most serious problems associated with land-based
activities are:
- alteration and destruction of habitats and ecosystems
- effects of sewage on human health
- widespread and increased eutrophication
- changes in sediment flow due to hydrological changes“.
The available knowledge demands to reduce pollution
of seas and oceans by nutrients. This knowledge has to be
converted into action now. The decisive question is however, whether political intension and financial power
world wide do support such a goal.
7 Acknowledgements
The authors most heartily thank Mrs. Monika Long
(FAL-PB) for editing and language revision of the paper.
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